U.S. patent application number 09/798843 was filed with the patent office on 2002-07-11 for pulping process.
Invention is credited to Bryant, Patrick S., Hutto, Dwane S., Sokol, John C..
Application Number | 20020088569 09/798843 |
Document ID | / |
Family ID | 23993337 |
Filed Date | 2002-07-11 |
United States Patent
Application |
20020088569 |
Kind Code |
A1 |
Bryant, Patrick S. ; et
al. |
July 11, 2002 |
Pulping process
Abstract
The present invention relates to a process for the removal of
lignin from lignocellulose containing material comprising treating
the lignocellulose containing material prior to a high-yield
pulping process with a delignifying gas comprising gaseous
compounds comprising at least one oxygen atom such as chlorine
dioxide containing gas.
Inventors: |
Bryant, Patrick S.;
(Woodstock, GA) ; Sokol, John C.; (Kennesaw,
GA) ; Hutto, Dwane S.; (Kennesaw, GA) |
Correspondence
Address: |
Lainie E. Parker
Akzo Nobel Inc.
Intellectual Property Department
7 Livingstone Avenue
Dobbs Ferry
NY
10522-3408
US
|
Family ID: |
23993337 |
Appl. No.: |
09/798843 |
Filed: |
March 2, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09798843 |
Mar 2, 2001 |
|
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09501384 |
Feb 9, 2000 |
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Current U.S.
Class: |
162/63 ; 162/65;
162/67 |
Current CPC
Class: |
D21C 1/04 20130101; D21C
1/00 20130101 |
Class at
Publication: |
162/63 ; 162/65;
162/67 |
International
Class: |
D21C 009/147; D21C
009/14 |
Claims
1. A process for the removal of lignin from lignocellulose
containing material comprising treating the lignocellulose
containing material prior to a high-yield pulping process with a
delignifying gas comprising gaseous compounds comprising at least
one oxygen atom.
2. A process according to claim 1, wherein the delignifying
comprises chlorine dioxide, nitrogen oxides, carbon dioxide,
sulphur dioxide or mixtures thereof.
3. A process according to claim 1, wherein the gas comprises
chlorine dioxide.
4. A process according to claim 3, wherein the charge of chlorine
dioxide is from about 0.5 kg active Cl.sub.2 per tonne oven dry
lignocellulose containing material up to about 300 kg active
Cl.sub.2 per tonne oven dry lignocellulose containing material.
5. A process according to claim 4, wherein the charge of chlorine
dioxide is from about 2 kg active Cl.sub.2 per tonne oven dry
lignocellulose containing material up to 100 kg active Cl.sub.2 per
tonne oven dry lignocellulose containing material.
6. A process according to claim 3, wherein the concentration of
chlorine dioxide in the delignifying gas is from about 0.05 up to
about 100% by volume.
7. A process according to claim 6, wherein the concentration of
chlorine dioxide in the delignifying gas is from about 0.05 up to
about 50% by volume.
8. A process according to claim 1, wherein the pressure during the
treatment with the delignifying gas is from about 10 kPa up to
about 500 kPa.
9. A process according to claim 1, wherein the temperature during
the treatment is from about 10 up to about 400.degree. C.
10. A process according to claim 1, wherein the lignocellulose
containing material prior to the treatment with the delignifying
gas is subjected to steaming and/or evacuation.
11. A process according to claim 1, wherein the treatment with the
delignifying gas is operated in batch or continuous mode.
Description
[0001] This application is a continuation of application Ser. No.
09/501,384, filed Feb. 9, 2000.
FIELD OF THE INVENTION
[0002] The present invention relates to a process for the removal
of lignin from lignocellulose containing material comprising
treating the lignocellulose containing material prior to a
high-yield pulping process with a delignifying gas comprising
gaseous compounds comprising at least one oxygen atom.
BACKGROUND OF THE INVENTION
[0003] In high-yield processes, or mechanical pulping processes as
they also are referred to, the objective is to disrupt the
structure of the lignocellulosic containing material in fragments
of variable dimensions by the use of mechanical treatment
optionally in the presence of chemicals.
[0004] High-yield pulps are produced by grinding or refining of the
lignocellulose containing material and thereby essentially all of
the fibres constituents are retained in the pulp.
[0005] High-yield pulping processes encompasses grinding, screening
and refining processes. In the grinding process, washed logs are
forced against a rotating grinding disk to tear the lignocellulose
containing material into small pieces which are then further
processed by screening or refining to produce mechanical pulp. In
the refining process, screened washed chips pass between rotating
disks or a rotating and stationary disk to shred the lignocellulose
containing material into pulp. The resultant pulp may then be
further refined, screened and cleaned to produce the desired
mechanical pulp.
[0006] One aspect of high-yield pulping is to rip or shred the
lignocellulose containing material into fibres which consumes
energy. This energy is measured as the power required to rotate the
grindstone or the refiner disk(s).
[0007] A significant portion of the total energy used in high-yield
pulping process is required to break or soften the lignin bonded to
the cellulose and hemicellulose fibres. Weakening or breaking down
the lignin structure prior to the grinding or refining process
results in significant reductions in the power requirement to
produce the finished high-yield (mechanical) pulp.
[0008] Energy, usually measured in terms of electrical power, is a
major component in the cost of producing high-yields pulps. Thus,
the pulp production cost increases directly with the cost of
energy.
[0009] Therefore, one advantage of the present invention is to
provide a pretreatment process that softens or breaks the lignin
contained within the lignocellulose containing material resulting
in a substantial reduction in the energy required to produce high
yield pulp.
[0010] U.S. Pat. No. 4,172,006 refers to the pretreatment of wood
chips with oxygen prior to adding a cooking liquor.
[0011] U.S. Pat. No. 4,750,973 relates to a process for reducing
carbohydrate losses in sulphate pulping of wood using sodium
hydroxides and sodium sulfide, wherein the wood is pretreated in
presence of water with oxygen gas and nitrogen oxides.
[0012] GB 567774 discloses a process for the treatment of
cellulosic raw material where wood chips are contacted with a
aqueous solution of a wetting agent prior to subjecting the chips
to a solution containing sodium chlorite thereby using sufficient
acid to insure the liberation of chlorine dioxide.
[0013] WO 8908165 refers to a method for the pretreatment of wood
chips with sulphur dioxide gas prior to alkaline deligification
operations.
[0014] DE 1049220 discloses a method comprising subjecting wood
chips to carbon acid before sulfite cooking.
[0015] JP 49020241 refers to a pulping process comprising the steps
of reacting chlorine dioxide or a mixture consisting of chlorine
dioxide and chlorine with wood chips in the presence of water
soluble cellulose derivatives and thereafter removing inter alia
the oxidised lignin by extraction.
[0016] U.S. Pat. No. 5,474,654 refers to a delignification process
where chlorine dioxide gas is used on pulp obtained from pulping
processes such as chemical kraft, sulfide or mechanical
processes.
[0017] Common to all prior art documents cited above is that the
pretreatment is carried out before a chemical pulping process.
[0018] U.S. Pat. Nos. 3,591,451 and 3,919,041 disclose the use of
gaseous chlorine dioxide subsequent a pretreatment step which may
be either mechanical, chemical or a combination thereof.
SUMMARY OF THE INVENTION
[0019] In accordance with the present invention it has surprisingly
been found that a substantial reduction in the energy required to
produce high yield pulp can be obtained by providing a process
according to the claims. More specifically, the invention relates
to a process for the removal of lignin from lignocellulose
containing material comprising treating the lignocellulose
containing material prior to a high-yield pulping process with a
delignifying gas, wherein the gas comprises gaseous compounds
comprising at least one oxygen atom.
DETAILED DESCRIPTION OF THE INVENTION
[0020] Suitable lignocellulose containing material used in the
present invention can be any lignocellulose containing material
derived from natural sources such as softwood, hardwood, gum,
straw, bagasse and/or bamboo. The physical state of the
lignocellulose containing material is not critical, however, a
physical state providing a large surface area is preferred that
maximises penetration of the delignifying gas and optionally
processing chemicals. Suitably, the lignocellulose containing
material is in the form of chips with a size which is governed by
the process equipment and process parameters.
[0021] Further advantages of the present invention are apparent
from the specification.
[0022] The lignocellulose containing material is suitably treated
according to any method known to the skilled artisan which renders
the diffusion of the delignifying gas within the fibre source to
the lignin more effective such as steaming and/or evacuation.
[0023] According to the present invention the lignocellulosic
material is treated with a delignifying gas comprising gaseous
compounds comprising at least one oxygen atom. Suitably, the
delignifying gas comprising chlorine dioxide, nitrogen oxides,
carbon dioxide or sulphur dioxide or mixtures thereof. Nitrogen
oxides include nitrogen monoxide, nitrogen dioxide, polymeric
oxides and double molecules thereof, e.g. N.sub.2O.sub.4 or
N.sub.2O.sub.3.
[0024] The delignifying gas mixture is suitably a non-liquid
containing gas.
[0025] According to one preferred embodiment the delignifying gas
comprises chlorine dioxide. The chlorine dioxide containing gas may
contain other gases such as nitrogen, oxygen, air or steam or
mixtures thereof. The chlorine dioxide containing gas may also
contain small amounts of chlorine, however, the gas is suitably
substantially free from chlorine, preferably having less than 10%
by volume, more preferably less than 1% by volume of chlorine.
[0026] The use of a delignifying gas such as a gas comprising
chlorine dioxide overcomes several unsolved problems. Treatment of
the lignocellulosic containing material with solutions containing
for example chlorine dioxide is limited by the rate of chlorine
dioxide diffusion through the solution to the fibre source followed
by the diffusion of the chlorine dioxide within the fibre source to
the lignin. The result is a slow delignification process that works
primarily on the fibre source surface and an aqueous effluent
stream containing chlorine dioxide, dissolved fibre components and
chlorides, which is difficult to treat in an environmentally
correct manner.
[0027] It has been found that a gas comprising chlorine dioxide
does not have the diffusion barriers that limit the process when a
solution is used. The gas passes rapidly and uniformly into the
fibre source resulting in even delignification throughout the
material. Furthermore, there are no aqueous effluent streams.
[0028] Preferably, the gas comprising chlorine dioxide is applied
on lignocellulose containing material free from any surrounding
aqueous solution. Preferably, the moisture content of the
lignocellulose containing material is from about 30 weight % up to
about 60 weight % based on oven dry material, more preferably from
about 40 up to about 50 weight %.
[0029] The chlorine dioxide containing gas employed in the present
invention is suitably produced using a chlorine dioxide generation
process as described in the U.S. Pat. Nos. 4,770,868, 5,091,166,
5,091,197 and 5,380,517, which all are incorporated by
reference.
[0030] The concentration of chlorine dioxide in the gas is not
critical for the invention. Thus, the lignocellulose containing
material may be treated with substantially pure chlorine dioxide
gas. The upper limit of the amount of chlorine dioxide, i.e.
chlorine dioxide comprised in the gas mixture, is purely set by
safety considerations. Suitable concentrations of chlorine dioxide
comprised in the gas mixture are from about 0.05 up to about 100%
by volume, more preferably from about 0.05 up to about 50% by
volume and most preferably from about 1 up to about 20% by
volume.
[0031] The gas comprising chlorine dioxide is generally applied in
amounts which renders a reduction in the energy required for the
production of pulp compared to a process where the lignocellulose
containing material has not been subjected to chlorine dioxide
prior to said high-yield process. Usually, increased applied amount
of chlorine dioxide comprised in the gas (mixture) increases the
degree of delignification. The charge of chlorine dioxide is from
about 0.5 kg/tonne up to about 300 kg active Cl.sub.2 per tonne of
oven dry material, more preferably from about 2 kg up to about 100
kg active Cl.sub.2 per tonne oven dry material and most preferably
from about 30 kg/tonne up to about 50 kg active Cl.sub.2 per tonne
oven dry material.
[0032] The present invention may be performed at any location prior
to high-yield pulping processes, i.e. mechanical pulping
processes.
[0033] According to a preferred embodiment the treatment with the
gas comprising gaseous compounds comprising at least one oxygen
atom is carried out prior to a refining process, suitably prior to
a first refining process.
[0034] The lignocellulose containing material may be treated with
the delignifying gas in any type of equipment. For practical
reasons the equipment should be gas tight. The treatment with the
gas comprising chlorine dioxide may also be carried out in the same
equipment (vessel) as is used for the subsequent pulping
process.
[0035] Suitably, the treatment is carried out in an equipment such
as a vessel which is essentially free from an aqueous solution,
i.e. the treatment is carried out in the absence of aqueous
solutions. By essentially free from an aqueous solution is meant
that a minor amount aqueous solution can be present during the
treatment with a gas comprising chlorine dioxide as long as the
removal efficiency of lignin is not significantly impaired, i.e. as
long as the overall diffusion (diffusion of the gas in respect of
the totality of material treated) of the gas containing chlorine
dioxide to the lignocellulose containing material is not
significantly impaired or as long as a reduction in the energy
required for the production of high-yield pulp is obtained compared
to a process where the lignocellulose containing material has not
been subjected to chlorine dioxide prior to said high-yield
process.
[0036] The delignifying gas such as a gas comprising chlorine
dioxide is suitably admixed with the lignocellulose containing
material in an equipment which is at any suitable pressure
including atmospheric, subatmospheric or superatmospheric
pressures. Suitably, the treatment is carried out at a pressure
ranging from about 10 kPa up to about 500 kPa, preferably from
about 50 kPa up to about 250 kPa. The most preferred pressure
ranges from about 80 kPa up to about 120 kPa.
[0037] The temperature during the treatment according to the
present invention is not critical and can be carried out at
surprisingly low temperatures including ambient temperatures. The
upper temperature level in the treatment is set by economical and
safety considerations. Temperatures may range from about 10.degree.
C. up to about 400.degree. C., suitably from about 15.degree. C. up
to 200.degree. C., more preferably from 20.degree. C. up to about
95.degree. C. and most preferably from about 25.degree. C. up to
about 90.degree. C. Suitable temperature ranges are also those
obtained by combining any of the lower temperature level of above
ranges with any of the higher temperature levels.
[0038] According to one preferred embodiment of the present
invention the lignocellulose containing material is pretreated
prior to being subjected to the gas comprising chlorine dioxide.
The pretreatment may be accomplished in the same equipment used for
the delignifying gas, yet, the pretreatment can also be performed
in any suitable equipment located upstream the treatment with the
delignifying gas. Suitably, the pretreatment includes various
steaming and/or evacuation processes. The pretreatment is believed
to open up the lattice structure of the lignocellulose containing
material thereby improving the diffusion of the delignifying gas
into the material.
[0039] High-yield or mechanical pulping processes are generally
pulping processes where the yield typically is from about 70 up to
about nearly 100% by weight based on total lignocellulose
containing material. Commonly, high-yield pulping processes are
referred to as stone groundwood (SGW), pressurised groundwood
(PGW), refiner mechanical pulp (RMP) and modifications thereof,
thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP) or
chemimechanical pulp (CMP). The basic principle in high-yield
pulping processes is to disrupt the wood structure in fragments of
variable dimensions by the use of mechanical treatments optionally
in conjunction with chemicals such as sulphite. Usually a refiner
is used, where wood ships are fed between two metal disks, of which
at least one disc is rotating, and the wood fibres are separated by
the action of grooves and bars located on the surface of the two
disks. Obviously, energy usage is high in high-yield pulping
processes, especially in TMP pulping processes.
[0040] Thus, one advantage with the present invention is that by
treating lignocellulose containing material prior to high-yield
pulping processes the input of energy in said pulping processes can
be significantly reduced.
[0041] The process may be operated in either batch or continuous
mode.
[0042] To further illustrate the invention the following examples
are provided. All parts and percentages are by weight unless
otherwise specified. Temperatures are in degrees Celsius.
EXAMPLE
[0043] In this example the total energy consumption for refining
untreated wood chips and wood chips treated with chlorine dioxide
containing gas prior to high yield pulping to specific Canadian
Standard Freeness (CSF) levels was measured.
[0044] Douglas Fir wood chips obtained from a commercial pulp
supplier were used. The samples were pulled at random from the chip
supply and were then mixed and separated into samples 1 and 2.
There was no special handling, separation or classification of the
chips prior to the experiment. The chips of sample 1 were treated
with the chlorine dioxide containing gas in a packed bed reactor
with a gas containing approximately 3% to 5% chlorine dioxide on a
volume basis. Approximately 20 grams of chlorine dioxide were used
to treat 1 kg of wood chips. The resulting treated wood chips were
then pre-steamed and mechanically refined to specific Canadian
Standard Freeness levels using a Sprout-Bauer 12-1 CP pressurized
laboratory refiner. The first stage refining involves size
reduction from chips to matchstick material and was conducted at
approximately 30% consistency. All subsequent refining stages were
performed at 15% consistency. Chip pre-steaming was conducted for 3
to 5 minutes by direct injection of 206,8 kPa (30 psig) steam. In
subsequent refining stages, the pulp was heated by steaming with
low-pressure steam 13,8-20,7 kPa (2-3 psig) by direct injection to
heat the wood to 100.degree. C. The energy consumption at each CSF
level was measured (table 1).
[0045] Wood chips from sample 2 which were not subjected to
chlorine dioxide treatment were pre-steamed and refined to the same
CSF levels using the same equipment and procedures as the wood of
sample 1 to establish a base energy consumption for the refining
process.
[0046] Table 1 shows the total energy requirement versus the CSF
for wood chips not subjected to a chlorine dioxide containing gas
(control) and wood chips treated with a chlorine dioxide containing
gas as outlined above (treated).
1 TABLE 1 Total Energy kWatt-hour/metric tonne CSF Control Treated
Delta % 750 876 532 39 700 969 580 40 650 1069 632 41 600 1177 689
42 550 1294 750 42 500 1423 816 43 450 1565 890 43 400 1723 973 44
350 1903 1067 44 300 2111 1175 44 250 2357 1303 45 200 2657 1459 45
150 3045 1661 45 100 3591 1946 46 50 4525 2432 46
[0047] Table 1 clearly shows a significant reduction in the energy
requirement when producing mechanical pulp using wood chips treated
with chlorine dioxide containing gas. In the commercially relevant
area, i.e. CSF between 50 and 150 ml, the energy requirement for
the treated chips is approximately 45% lower than the untreated
chips.
[0048] The invention is further illustrated by the following
claims, which, however, do not limit the scope thereof.
* * * * *